1. Field of the Invention
The present invention relates in general to the art of bearing assemblies and in particular to an improved bearing section for a downhole drilling motor that is carried near the end of a rotary drill string and actuated by the downflowing drilling fluid to drive a rotary drill bit for the drilling of oil and gas wells and the like.
The conventional U.S. system of oil well drilling involves the rotation of a string of drill pipe with a rotary drill bit located at the end of the drill string. Power from a motor or engine at the surface is transmitted to the bit by rotating the entire drill string. During drilling, a drilling fluid, generally called drilling mud, is pumped downward through the inside of the drill string and out through ports in the drill bit. The fluid then carries the material loosened by the drill bit back to the surface through the annular space between the drill pipe and bore hole. Many and varied circumstances make it desirable to drive the drill bit at speeds independent of the rotation of the drill string. A downhole motor is usually attached at or near the bottom of the drill string to accomplish such independent rotation of the drill bit. The motor may be electric or hydraulic. If hydraulic, it may be either a turbine or a positive displacement vane loader or it may be other types. All motors must have certain essential elements. First is a power section with a stator and a rotor which produce the torque and rotation between them. Next is a bearing section that includes thrust and radial bearing supports between the stationary and rotating members. Finally, there must be a flow path for the drilling fluid from the drill string to the drill bit, which path may be through the power section and at least partially through the bearing supports for lubrication. It will be realized that the drilling fluid and its contaminates are hostile to the function and life of the bearings and, therefore, control of the drilling fluid through the bearing section is significant to motor function, life, and overall drilling cost.
Such a system would require diversion of the drilling fluid flow through the bearing section with minimum erosion. Further, such control would substantially eliminate drilling fluid erosion at the intersection of the lower bearing section and its associated power or drive section. Further, the bearing section should be so constructed as to reduce thread fatigue breakage due to oscillating load conditions at the intersection of the lower bearing section and its top drive shaft. The bearing assemblies could be further protected if the drill pipe inner diameter drilling fluid flow could be diverted from direct flow through the bearing assembly and yet allow the drilling fluid to serve as the lubrication. Further, it would helpful to reduce the hydrostatic pressure applied to the bearing assemblies.
2. Description of Prior Art
To overcome such problems, in the prior art such as disclosed in U.S. Pat. No. 4,546,836, the bearing section included a series of elastomer flow restrictor elements each responding to increased fluid pressure by reducing the flow area therethrough thus controlling the fluid flow through the bearing within a narrow range of flow rates.
In U.S. Pat. No. 4,577,704, the bearing system includes a main thrust and radial bearing system having means for sealing the bearings in oil at equal or a slight pressure above that of the drilling mud inside the drill pipe. Thus the fluid seals and bearings were insulated from all possibility of contact with drilling cutting fluid and its associated debris created by the drilling operation.
In like manner, in U.S. Pat. No. 4,114,703, a lubricant chamber for the bearings is sealed with a piston that is pressurized by the drilling fluid flowing through the bearing section.